1. Field of the Invention
The present invention relates to a mobile communication apparatus suitable for use with a combination type portable telephone set which can transmit and receive in accordance with a plurality of transmission/reception systems.
2. Description of the Related Art
In mobile telecommunication wherein a portable telephone set or the like is used, radio wave propagation across a plurality of obstacles is expected upon transmission/reception, for example, in an urban district. Arriving waves having passed through a plurality of paths suffer from significant fading, and as a result, communication failure or communication interruption in mobile communication by standing waves originating from such fading occurs. Therefore, in mobile communication, a diversity system is sometimes used wherein two or more antennae are used for transmission/reception and one of received waves which has a higher level is selected or two waves are combined so that the probability in deterioration of the reception quality may be reduced when compared with another case wherein a single received wave is use. Generally, a portable telephone set uses selection combining wherein only that one of a plurality of fading waves inputted individually using a plurality of antennae which has a maximum envelope level is selectively received.
Conventionally, such a portable telephone set of the PDC (personal digital cellular)/PHS (personal handyphone system) combination type employing the diversity system as shown in FIG. 5 is known. Referring to FIG. 5, the conventional portable telephone set of the PDC/PHS combination type shown includes a PHS transmitter-receiver 30A, a PDC transmitter-receiver 30B, and a CPU 312 for controlling the transmitter receivers 30A and 30B. The PHS transmitter-receiver 30A includes a PHS antenna circuit 301 having a single antenna, a PHS reception circuit 302 and a PHS transmission circuit 303, a transmission/reception switching circuit 301a, a phase-locked loop (PLL) IC 304, and a PHS modulation/demodulation circuit 305. Meanwhile, the PDC transmitter-receiver 30B includes a PDC antenna circuit 306 having two antennae, an antenna switching circuit 307, a PDC reception circuit 308 and a PDC transmission circuit 310, a PDC local circuit 309, and a PDC modulation/demodulation IC 311.
It is expected that such a portable telephone set of the combination type as described above is used such that both of transmission/reception systems operate for reception in order to make up for drawbacks of both of the PDC and PHS signal systems particularly in a reception waiting state. Generally, the PDC system is more advantageous upon high speed movement of the telephone set or in terms of the extent of a service area, and the PHS is more advantageous when the telephone set is used on a subway or on an underground market. Further, where such a great number of other users use telephone sets that connection of a telephone call cannot be established readily, one of the systems which has a comparatively great number of free circuits can be selectively used for a telephone call.
When such a portable terminal set of the combination type as described above is designed, a control system is sometimes used wherein, in order to suppress power consumption or from some other object, operation of the two systems is not controlled finely in a waiting state, but when communication is proceeding using one of the PDC and PHS transmission/communication systems, the power supply to a radio section of the transmission/reception system which is not in use is disconnected.
However, the conventional portable telephone set of the combination type has the following problems.
In particular, the PDC and PHS transmission/reception systems are complicated in control for establishment of synchronism due to measures for prevention of tapping and so forth, and usually they perform transmission/reception operations independently of each other until it is confirmed that reception data from one of the transmission/reception systems is a telephone number of the telephone set of the combination type itself. Accordingly, when either one of the PDC and PHS transmission/reception systems performs a transmission/reception operation such as position registration, the other system side may be at a reception timing of intermittent reception. As a result, the conventional portable telephone set of the combination type is disadvantageous in that one of the two systems cannot perform reception accurately and may possibly come out of synchronism.
Further, if synchronism is lost, then operation such as continuous reception is performed in order to establish synchronism again, resulting in another disadvantage that unnecessary power is dissipated.
It is an object of the present invention to provide a mobile communication apparatus of the diversity system including a plurality of transmitter-receivers of different transmission/reception systems wherein a drop of the antenna reception sensitivity of one system by an output from the antenna of the other system is minimized and the synchronism keeping accuracy is augmented and besides unnecessary dissipation of power is prevented.
In order to attain the object described above, according to the present invention, there is provided a mobile communication apparatus, comprising a first transmitter-receiver for outputting, upon transmission, a gain decrease instruction, the first transmitter-receiver having a transmission antennae, a second transmitter-receiver including a plurality of antennae and operable for selecting one of the plurality of antennae which has a high antenna gain so as to be used for reception, the first and second transmitter-receivers employing different transmission/reception systems from each other, and gain adjustment means for decreasing an antenna gain of one of the plurality of antennae of the second transmitter-receiver which has a high degree of coupling to the transmission antenna of the first transmitter-receiver in accordance with the gain decrease instruction.
The gain adjustment means may operate in response to a transmission control signal from the first transmitter-receiver.
The gain adjustment means may be a Schottky barrier diode which is connected, on a cathode side thereof, to that one of the plurality of antennae of the second transmitter-receiver which has a high degree of coupling to the transmission antenna of the first transmitter-receiver and connected, on an anode side thereof, to the first transmitter-receiver and is turned on in response to arrival of the gain decrease instruction.
Alternatively, the gain adjustment means may be a variable capacity diode which is connected between the first transmitter-receiver and that one of the plurality of antennae of the second transmitter-receiver which has a high degree of coupling to the transmission antenna of the first transmitter-receiver and is turned on in response to arrival of the gain decrease instruction.
The first transmitter-receiver may be a transmitter-receiver of the personal handyphone system, and the second transmitter-receiver may be a transmitter-receiver of the personal digital cellular system.
Where a mobile communication apparatus having such a construction as described above is incorporated in a portable telephone set, the portable telephone set becomes a portable telephone set of the combination type. In this instance, preferably the antennae employ a space diversity system and selective combining is used as a combination reception method.
Where the present invention is applied to a portable telephone set of the PDC/PHS combination type, when the PHS section transmits during intermittent waiting of the PDC section, the gain of one of the two PDC antennae which exhibits higher input power of a PHS transmission wave, that is, the gain of the antenna which has a higher degree of coupling to the PHS antenna, is decreased while the other antenna which exhibits lower input power of the PHS transmission wave, that is, the antenna which has a lower degree of coupling to the PHS antenna, is selected by the antenna diversity. Consequently, sensitivity deterioration by high input sensitivity suppression upon PHS transmission of the PDC reception section which has a short reception interval and includes the two antennae can be minimized.
With the mobile communication apparatus having the construction described above, although otherwise there is the possibility that the sensitivity may be deteriorated when the PHS section transmits during intermittent waiting of the PDC section, since the PDC antenna which has a lower degree of coupling to the PHS antenna is selected, the deterioration amount when sensitivity deterioration occurs can be minimized. Consequently, the mobile communication apparatus is advantageous in that the accuracy with which synchronism of the PDC section can be kept is augmented.
Further, if synchronism is lost, then usually a continuous reception operation is performed to try to detect a synchronizing signal. However, with the mobile communication apparatus, since synchronism of the PDC section can be kept, there is no necessity of performing continuous reception. Consequently, the mobile communication apparatus is advantageous in that unnecessary dissipation of power can be suppressed.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements are denoted by like reference symbols.